Boston, MA, is one of the largest metropolitan areas in the United States. The city itself contains over 600,000 people; but with all of the surrounding cities taken into account, the population of the area exceeds 4 million. The city also attracts more than 12 million visitors each year. Given these numbers, there's no wonder transportation is a large concern.
The Massachusetts Bay Transportation Authority (MBTA) operates the oldest and fourth largest transportation system in the country.
"The T", as it's known locally, was created in 1964 to run the already functioning transit system. Today, it provides transportation to the entire greater Boston area by means of subways, buses, ferries and commuter rail lines.
The commuter rail offers train service to out-lying points west, north and south of Boston, including Providence, RI. It is owned by the MBTA, but managed and operated by the Massachusetts Bay Commuter Railroad Co.
When the MBTA decided to extend the existing commuter rail line down the south shore, from Braintree all the way to Scituate, it became evident it would involve far more than simply laying down 18 miles of new track. The $250 million "Greenbush project" faced a variety of challenges almost immediately.
Bypass crucial to completion
One of many concerns was a decision regarding the functionality of a stretch of 48-in. pipe that belonged to the Massachusetts Water Resource Authority. The stretch of pipe was part of a combined sewer line - a system that allows general public and industrial waste to combine with ground water runoff when conventional sewer systems are at capacity during periods of heavy rainfall.
As it turned out, the pipe was positioned at the exact point where a portion of the extended rail line was planned. In order to complete the rail extension, the sewer line would have to be bypassed and rebuilt at a lower elevation without disturbing the local population of the area or causing environmental impact.
A large volume of water would have to be re-routed before reconstruction of the pipe could begin. Cashman/Balfour-Beatty (CBB), the company entrusted with completing this undertaking, contacted Baker Pumps to coordinate the bypass operation.
There was little margin for error. "With a bypass, what we do is interrupt the line," explains Carroll Hunnewell, a regional manager with Baker Pumps. "We plug it off and it has no place to go. If we can't pump it, it backs up. Then there is a chance that it can come out in the street or back up into homes."
There could also be financial repercussions. "Any problem would have been a big mess to clean up. And with the environmental issues at stake, we could have faced fines for any violation," says Julie Power, a project engineer who worked on the Greenbush project for CBB. "Once the pumps were installed, we needed to ensure they would remain reliably operating to their maximum capacity so the construction team would be able to go in and complete their work in a timely fashion."
Pumping in all kinds of weather
While pumps from several different manufacturers were considered, the project team ultimately settled on The Gorman-Rupp Co.'s Prime Aire pumps. These pumps operate with a patented priming system engineered to eliminate weepage. They also feature a dual-suction side capability, a compressor-over-pump and an abrasive-handling seal.
To execute the pumping operation, Baker Pumps designed a siphon to direct the water down, then back up a 5-ft. elevation. The operation implemented seven 12-in. pumps (six primaries and one backup) that attached directly to seven 14-in. suction lines, with water being discharged 750 ft. away into the siphon chamber. The company also had to deal with a 22-ft. lift in elevation from the water level to the pump centerline at its highest point.
The presence of homes and shops in the area also made noise a primary concern. To address this, Baker Pumps developed a soundproof barrier around the project using sound-absorbing curtains, which cut noise level by more than 30% at a distance of 30 ft.